In disc drives, a recording media sector typically includes a preamble (a 2T data pattern), a leading sync mark, host data, EDC (Error Detecting Code), ECC (Error Correcting Coding), and flush bits. The data is coded so that it maintains certain properties necessary for the proper operation of a readback channel. The flush bits written to the media force the channel to continue processing data until the final coded host data makes it through the circuitry. This function is commonly referred to as “flushing the channel.” The leading sync mark, data coding, and flush bits affect the format efficiency of the drive. Format efficiency is the ratio of the number of original host data symbols to the number of data symbols actually written to the disc. As a rule of thumb in contemporary products, a 1% improvement in format efficiency translates to about 0.18 dB improvement in signal-to-noise ratio (SNR), a significant improvement in a read channel. The use of a data format in which a leading sync mark must be substantially correct in order for data to be read, reduces the format efficiency and also increases the number of errors that must be either handled or mapped out of the drive by a flaw scan procedure.
A method and apparatus are needed that can increase format efficiency by reducing or eliminating the need to read a leading sync mark in a data channel. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.